A Word of Observing Caution

This June 5th, we have an opportunity to see a rather rare astronomical event, the transit of Venus, when the planet Venus gets between our Earth and the Sun. The result is that we can see the small, round dot of Venus’ silhouette traversing across the bright disk of the Sun. This event has both tremendous scientific and historic significance in astronomy, but it also has its dangers.

The Sun is bright, something we all know. We shouldn’t look at it without proper protection, namely solar filters. One should definitely NOT look at the Sun through a telescope unless one employs a full aperture solar filter which has been approved for visual solar observing. Failure to adhere to this warning means instantaneous and irreversible damage to your eyes.

Do not employ dark glass for a solar filter.

Fogged film is not an appropriate solar filter.

Dark sunglasses are not appropriate solar filters.

Welding glass used at the eyepiece of a telescope is NOT a safe solar filter.

If you are interested in seeing the transit using safe equipment, and you are not sure what to purchase, you have some options:

Visit your local astronomical society or planetarium and ask the astronomers there for equipment suggestions.

An affordable solution to see the transit without optical aide would be to purchase some “Eclipse Glasses” from a source like Amazon. This one comes in a package of 5: HERE. WARNING!!! DO NOT USE THESE IN COMBINATION WITH BINOCULARS OR OTHER UNFILTERED OPTICAL SYSTEM. These cannot withstand the light and heat concentration put out by optical instruments. These are for wearing alone.

Many local astronomy clubs, societies and associations will be setting up equipment for the public to use in order to view the event. The New Hampshire Astronomical Society is doing just that and will post information at http://www.nhastro.com as they prep for multiple observing sites throughout the state on the afternoon of June 5th.

From the east coast (New Hampshire), the Sun will be setting as the transit begins. Some observatories, including the one at Phillips Exeter Academy will not be able to see the Sun through trees and houses which will obstruct the view. In these cases the observatory will remain closed, and a portable observing location would be set up elsewhere at a higher elevation with a clear westerly view. Stay tuned to your local club’s/observatory’s websites for more details.

Historical Significance:

Transits were one of the earliest observational methods used to determine an accurate measure of the Astronomical Unit, the average distance between the Earth and the Sun. Using two widely separated observing stations and precise timepieces, observers would note the time difference between the start and end of the transit. Using then the mathematics of triangles (parallax) and Kepler’s Laws of Planetary Motion, the distance could be calculated.

The earliest observation of this type actually involved the planet Mercury transit of the Sun in 1676. A rather famous astronomer (you know the name!), Edmund Halley, made observations from St. Helena. One other set of observations was made elsewhere, but the mathematics proved to show some serious inaccuracies. In 1761 (and by this time Halley had passed away), there was a Venus transit. Many sites were established to observe the event. In 1769, another Venus transit was observed, and also created a large scientific collaboration between countries. This was also the first event which marked Captain James Cook’s initial voyage through the Pacific. Future transits were then observed, the last in 2004. The next one will be in 2117 (December 10-11), so this event in June 2012 will be the last we are able to see in our lifetimes. To help you plan your transit, see the two images below. The first is from the Wikipedia article Transit of Venus, 2012. The second comes from the NASA Eclipse Website.

Hi Sally, The images are available directly from NASA’s website. As long as NASA is referenced as the author, anyone can grab and reprint for not-for-profit applications. You should to nasa.gov for their policy on reprints. ~john